Connor Alvarez, Taylor Chavez, James Christiansen-Salameh, and Deanna Watson
This report outlines the creation and development of a portable and adjustable stander designed to suit the needs of Jack, a young boy diagnosed with a disease called Optic Nerve Hypoplasia. The purpose of the stander concept is to help Jack maintain proper Achilles tendon elongation in order to prevent the need for painful surgical tendon elongation operations. The stander that Jack currently has is bulky, heavy, and somewhat immobile, thus the Mobi-S Stander team set out to design a device that could easily be used and transported between places of use while maintaining functionality. In order to improve upon the design of his current stander, compactness, portability, strength, and user comfort were factors taken into consideration when developing the Mobi concept. Upon completion of the final product, the LMU Assistive Tech team will present the Mobi-Sheldon (Mobi-S) desk stander to Jack and his family.
The client for the production of the Mobi-S Stander is a ten-year-old boy named Jack who has been diagnosed with a disease called Optic Nerve Hypoplasia (ONH). ONH is the underdevelopment or absence of the optic nerve combined with possible brain and endocrine abnormalities. This disease affects his vision, his brain, his speech, fine motor skills, and the natural development he needs as a young boy (1). Jack currently relies on a wheelchair for transport, but his long-term goal is that one day he will have the strength he needs to walk on his own. In order for Jack to reach this goal, he needs to stand more often throughout the day. Standing is crucial for Jack because it allows his Achilles tendon to stretch which helps to prevent the need for an operation called Precutaneous Achilles Tendon Lengthening (2). This is a painful procedure that could debilitate him for several weeks, greatly impacting Jack’s progress toward his goal. A stander is a current Assistive Technology device that aids Jack in strengthening his muscles. Standers also provide health benefits such as enhanced respiratory function, development of appropriate alignment of the spine, hips, knees and ankles and the improvement of social interaction (3).
Jack’s current stander provides the support he needs around his waist, allowing him to keep weight on his feet without losing balance, however, this device is not easy to transport, and is becoming too small to fit Jack. Jack’s mother requested a device that would support his waist similar to the way his current stander does, while adding adjustability for his size as he grows and portability for travel. These features can be useful to anyone who requires a stander for muscle strengthening (4).
Jack desires a waist only, portable stander that can support his weight, adjust as he grows in size, and attach to a variety of tables.
Creative solutions were key to developing this unique concept for a stander. Basic shapes were used as the premise for the design in order to meet all of the desired functions. Once the requirements were believed to be met with the projected design, the components were manufactured in SolidWorks and parasolid files were created for machining in a HAAS mini mill at Loyola Marymount University. The team anticipated creating a machined prototype at the speed of rapid prototyping, but quickly learned the impossibility of that task. What they thought would take only a few weeks to create in reality took them several months, but once they started cutting, they chose to continue because time and money had already been spent to create the prototype. Once this was realized, the team chose to make the prototype as efficient as possible so that it could be used as a final product.
After several design iterations the first prototype of the Mobi-S Stander was completed. The Mobi-S is a combination of a prone and vertical stander; it allows Jack to have upper extremity use, remain supported at the hips, and get used to his own weight (5). This is accomplished via two side support pads. A belt wraps around the two pads, applying moderate force around Jack’s waist to ensure that he is supported when standing. The rest of the assembly is designed to adjust the pads to the desired position, and attach to the table via two metal square clamps.
Material choice is crucial to the design to ensure enough strength to support the high forces Jack may exert on it, and remain light enough to easily transport. Aluminum 6061-T6 was chosen as the material for most of the components due to its high strength to weight ratio. However, a steel alloy was used for some internal pieces due to the material resistances from aluminum interacting with aluminum.
Components For Adjustability
Securing the device to tables was a challenge because there are variety of lengths, heights and depths of tables. The initial clamps failed in testing due to improper welds and small tube diameter unable to withstand the forces applied in testing. Therefore new clamps machined out of a solid aluminum block into a simple U shape were designed to increase strength. These thick, one piece clamps are much stronger and still attach to a variety of tables.
To account for changes in table height as well as Jack’s increase in height over time (estimated growth to six feet tall), vertical extensions were designed to lock at certain height increments. Pads clamped onto elliptical bars that adjust at the waist via a knob account for changes in waist size over time. The elliptical shape of the bars is a beneficial design as it prevents rotation and ensures that the supports will maintain the correct orientation to support Jack’s sides.
A similar pad and belt assembly that Jack liked from his previous stander was incorporated into this design. In case of belt failure, a back bar was included as an added safety feature. The back bar and pad assembly can be inserted into the device once Jack is secured in the belt. If the belt fails, Jack’s weight will be supported by the back bar.
In the case of a slippery table, the clamps may not provide enough force to keep the device from slipping, therefore another safety feature that can be added is a table strap. The strap wraps around the device and the far end of the table, and is tightened via a ratchet clamp. Once tightened, the device will not rely strictly on friction between the table and clamps to hold it in place.
Components For Portability
The device could be easily transported if it could be folded to a size that could lay flat in the bottom of a suitcase. To achieve this position, the clamps fold inward, and the vertical extensions downward in accordance with the rotation of the pivot pieces. The rotation components are secured via pull pins. These pins restrict the motion of the various components so that they do not fold at improper times. Since the vertical extensions endure a greater stress than other areas on the device, an added key feature was incorporated into the design for double safety measures. The key is attached to the pivot pieces which keep them locked in the main channel at all times, as well as secure the vertical extension pieces in the upright position.
As was previously stated, the Mobi-S concept was initially designed to be a prototype. While the design is still in the prototype phase, it is functional and able to be used as a final product. The clamps have been tested on a variety of desks and the clamping force is consistently strong even on slippery surfaces. The additional straps to be used for securing the assembly are not essential, but will still be provided to Jack when he uses the product. The tolerances surrounding the pull pins are slightly too large causing unwanted motion of the various components. That tolerance in addition to the slight tolerances on each machined piece causes the parts to move more than necessary when the stander is assembled. However, once someone is standing between the pads and strapped in place, these tolerances are beneficial as they relieve some of pressure and stress on the pins and keys holding up the assembly. The back bar presented challenges to the assembly. The aluminum of the bar sliding against the aluminum of the vertical extensions caused the material to slightly warp due to the friction. To fix this problem, the holes and bar were filed down to decrease the amount of contact between the two, and quick-release clamps were installed on each end to prevent the bar from sliding back on to the floor. The design has been tested by the LMU design team, and has proven to be strong, secure, and comfortable. The design meets all of the necessary requirements put forth by Jack and his mom; Jack has seen a model of the device and is thrilled to use it soon.
Loyola Marymount University (LMU) hosts an excellent machinist who offers complimentary service for student projects; this saved hundreds of dollars while creating this prototype. The ability to work hand in hand with the in house machinist and student assistants is what allowed the prototype to be used as a functioning device. Realistically, the machining process used would not be an efficient way to design a prototype nor the final design as machining costs and labor are quite expensive. Most of the parts of the assembly were machined at LMU, but materials and fixtures were purchased at retailers such as Home Depot, M & K Metals, FixtureWorks and McMaster Carr. For the bending and welding required for this design, the parts were taken to local A&M Welding and Aero Welding and Manufacturing. The total cost of parts with machining, welding, bending and fixtures totaled to approximately $740.00 as outlined in the table below:
Table 1: This table gives the approximated values of the material and production costs of the device.
|Table: Approximated Totals of Cost Analysis|
|Welding||Aero Welding and Manufacturing||$40|
|Home Depot (belt)||$30.00|
Should this product be redesigned, i.e. The Mobi-S2, there are many changes that could reduce the cost of material and production as well as improve product efficiency. It would be beneficial to cast the aluminum features instead of machine them. Combining necessary features into the mold of a cast would reduce the amount of moving parts and manufacturing time. These changes could also improve the aesthetics of the overall part resulting in a less bulky design with a smoother finish. The fixtures are strong, but further developing an idea of push button features as opposed to pull release features may make the assembly easier to use as well.
(1) Children’s Hospital Los Angeles. “Optic Nerve Hypoplasia.” Chla.org. Children’s Hospital Los Angeles, n.d. Web. http://www.chla.org/site/c.ipINKTOAJsG/b.6051827/k.9DAD/Optic_Nerve_Hypoplasia_in_Children__ONH_Eye_Care__The_Vision_Center.htm#.UlIcslshMmk
(2) ” Percutaneous Achilles Tendon Lengthening.” Percutaneous Achilles Tendon Lengthening. FootCare MD, n.d. Web. Mar. 2014. <https://www.aofas.org/footcaremd/treatments/Pages/Percutaneous-Achilles-Tendon-Lengthening.aspx>. Mar. 2014
(3) Pediatric Stander information: http://www.1800wheelchair.com/asp/view-category-products.asp?category_id=679
(4) Jack, Ivey, Sami and Miss Chavez, personal conversations, September 25, 2013, October 5, 2013
(5) 1800WheelChair. 1800WheelChair. Www.1800WheelChair.com, n.d. Web.
Rifton “Standing Aids” http://www.rifton.com/resources/articles/2001/february/standing-aids
Jack and Ivey Van Allen
Drs. Nader Saniei and Matthew Sinisawski– LMU Professors
John McLennan and Joseph Foyos – LMU Machinists
Derek Lorenzen, Sarah Yamamoto, Jonathan Guerra—Student Assistant Machinists
Funding provided by LMU Seaver College of Science and Engineering